Abstract

Iron oxide nanoparticles are among the most widely used and characterized magnetic
nanoparticles. However, metal alloys such as superparamagnetic iron-platinum particles
(SIPPs), which have better magnetic properties, are receiving increased attention.
Scalable techniques to routinely synthesize SIPPs in bulk need further study. Here,
we focus on the role played by the fatty amine ligand in the formation of the bimetallic
FePt nanocrystal. More specifically, we compare the effect of varying lengths of fatty
amine ligands on the shape, structure, uniformity, composition, and magnetic properties
of the SIPPs. We synthesized SIPPs by employing a ‘green’ thermal decomposition reaction
using fatty amine ligands containing 12 to 18 carbons in length. Greater fatty amine
chain length increased the polydispersity, particle concentration, iron concentration,
and the stability of the SIPPs. Additionally, longer reflux times increased the diameter
of the particles, but decreased the iron concentration, suggesting that shorter reaction
times are preferable. Fourier transform infrared spectroscopy of the SIPPs indicates
that the ligands are successfully bound to the FePt cores through the amine group.
Superconducting quantum interference device magnetometry measurements suggest that
all of the SIPPs were superparamagnetic at room temperature and that SIPPs synthesized
using tetradecylamine had the highest saturation magnetization. Our findings indicate
that the octadecylamine ligand, which is currently used for the routine synthesis
of SIPPs, may not be optimal. Overall, we found that using tetradecylamine and a 30-min
reflux reaction resulted in optimal particles with the highest degree of monodispersity,
iron content, stability, and saturation magnetization.